Foam laminate system for semiconductor wafers

ABSTRACT

A cushion-like device is provided for the transportation of semiconductor wafers. The device includes an interior formed from polyethylene closed cell foam that utilizes a foaming agent that imparts minimal alkanes and cations into the polyethylene foam material. An electrostatic discharge dissipative polyethylene film surrounds the foam interior and is joined thereto by hot melt EVA material. An array of apertures of approximately 0.010 inch diameter and less than 0.25 inch spacing is formed in the film to allow the foam to compress upon impact.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a foam laminate system for use insemiconductor wafer portion, particularly from the front-end to anassembly location.

2. Description of the Prior Art

The transportation of semiconductor wafers, particularly transportationfrom the front-end to an assembly location, which typically may involvea trans-oceanic voyage, presents a set of challenges. Mechanical andelectrostatic protection must be provided. Contamination levels must bekept low to prevent the introduction of ions that, in combination withmoisture vapor, generate corrosion, pitting and/or transistor inversion.Extreme cleanliness required during the shipping of the semiconductorwafers. Similarly, mechanical protection of the semiconductor wafersduring transportation can be problematic if the wafer container is notcompletely full.

OBJECTS AND SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide acushion-like element for the transportation of semiconductor waferswhich maintains the low contamination levels required for suchtransportation.

It is therefore a further object of the present invention to provide acushion-like element which provides mechanical and electrostaticprotection to semiconductor wafers during transportation.

These and other objects are attained by providing a cushion with acylindrical interior formed of closed cell polyethylene foam, typicallyone quarter to three eighths of an inch thick, with a diameterapproximately equal to the diameter of the semiconductor wafers to betransported. A thin outer surface of electrostatic discharge (ESD)dissipative polyethylene is laminated to the polyethylene foam interiorby hot melt EVA adhesive. The exterior surface is perforated with smallapertures, typically less than 0.010 inches in diameter, to allow forcompression upon impact. The ESD dissipative polyethylene is heat wirecut to seal the ends about the periphery of the cushion.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and advantages will become apparent from the followingdescription and from the accompanying drawing, wherein:

FIG. 1 is a top plan view of the cushion-like device of the presentinvention.

FIG. 2 is a cross-sectional view along plane 2-2 of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings in detail wherein like numerals indicatelike elements throughout the several views, one sees that FIG. 1 is atop plan view of the cushion-like device 10 of the present invention.The cushion-like device 10 is symmetric so that FIG. 1 could likewise bea bottom view. Device 10 is cylindrically shaped with a diameterapproximately equal to the diameter (typical diameters include, but arenot limited to, eight or twelve inches) of the semiconductor wafers tobe transported. As shown in FIG. 2 the interior of device 10 is formedby a shallow cylindrically shaped portion 12 of polyethylene closed cellfoam which is typically neither treated nor dyed. The closed cell foamof portion 12 uses a foaming agent that imparts minimal alkanes andcations into the polyethylene foam material. Portion 12 of polyethyleneclose cell foam is typically one quarter to three eighths of an inchthick, but those skilled in the art, after review of this disclosure,will recognize that different thicknesses may be appropriate for variousapplications. The exterior of device 10 is covered with antistatic film(or laminate) 14. Antistatic film 14 is typically Richmond/Valeron®material, such as 1207 LLDPE Laminate Grade Film (86-R0438) which issold by assignee Illinois Tool Works Inc., using the specificationnumber 86-R0438 which details the formulation and property requirementsfor this antistatic film. Antistatic film 14 is typically 0.003 inchesthick and includes perforations 16 which typically are spaced less thanone fourth of an inch apart and have a diameter of 10 mils (0.010inches). This allows compression of portion 12 of polyethylene closedcell foam while maintaining the required clean environment around device10. Antistatic film 14 is secured to portion 12 of polyethylene closedcell foam by a laminating glue which is a hot melt EVA material that islikewise substantially free of cations and alkenes and is highlycompatible to polyethylene materials. As shown in FIG. 2, the antistaticfilm 14 is cut and heat sealed around the edges to form circularperipheral seam 18 thereby minimizing particulation of the foam uponaging. The antistatic film 14 typically provides electrostaticdissipative characteristics to both sides of portion 12 of polyethyleneclosed cell foam at low voltages, such as ten volts.

The cushion-like device 10 is designed to generate contamination levelsbelow 50 ppm (leachable alkanes, anions, halogens, ammonias or cations)as detected through leach testing at 60°0 and 90° Centigrade testing atone hour soak durations, as well as organic and inorganic analysis. Thelow organic/inorganic and acid compound material contamination reducesion contamination, pitting and corrosion on tight geometry 90 nanometer(and below) semiconductor wafers during shipping.

In order to use cushion-like device 10, the user typically placesseparations (not shown) between successive semiconductor wafers (notshown). A separator which is particularly well adapted for thisapplication is disclosed in U.S. provisional application Ser. No.______, filed on Jul. 13, 2004, entitled “Scribed Interleaf SeparatorWafer Packaging”. The cushion-like device 10 is placed at one or bothends of the stack of semiconductor wafers and separators and theresulting stack is placed into a container adapted for semiconductorwafer transportation. A container which is partially well adapted forthis application is disclosed in PCT/US04/14659, filed on May 10, 2004,entitled “Wafer Box with Radially Pivoting Latch Elements”. Theappropriate number and thickness of cushion-like devices 10 are chosenso that the semiconductor wafers are mechanically constrained within thecontainer.

Thus the several aforementioned objects and advantages are mosteffectively attained. Although a single preferred embodiment of theinvention has been disclosed and described in detail herein, it shouldbe understood that this invention is in no sense limited thereby and itsscope is to be determined by that of the appended claims.

1. A device for cushioning semiconductor wafer, comprising: a foaminterior; and a film surrounding said foam interior, said film havingantistatic characteristics and apertures to allow for compression ofsaid foam interior upon impact.
 2. The device of claim 1 wherein saidfoam interior comprises closed cell polyethylene foam.
 3. The device ofclaim 2 wherein said closed cell polyethylene foam utilizes a foamingagent which imparts minimal alkanes and cations to said closed cellpolyethylene foam.
 4. The device of claim 1 wherein said foam interioris cylindrical with a thickness substantially in the range of onequarter to three eighths of an inch thick.
 5. The device of claim 1wherein said film is secured to said foam interior by hot melt materialwhich is substantially free of cations and alkanes.
 6. The device ofclaim 1 wherein said film is an electrostatic dissipative polyethylene.7. The device of claim 6 wherein said film is approximately 0.003 inchesthick.
 8. The device of claim 7 wherein said apertures are approximately0.010 inches in diameter and are spaced less than 0.25 inches apart. 9.The device of claim 1 wherein said film includes a plurality of pieceswhich are joined together by a seam formed by heat sealing.